Abstract

Using 230.2 fb(-1) of e(+)e(-) annihilation data collected with the BABAR detector at and near the peak of the Upsilon(4S) resonance, 489 +/- 55 events containing the pure leptonic decay D-s(+)->mu(+)nu(mu) have been isolated in charm-tagged events. The ratio of partial widths Gamma(D-s(+)->mu(+)nu(mu))/Gamma(D-s(+)->phi pi(+)) is measured to be 0.143 +/- 0.018 +/- 0.006 allowing a determination of the pseudoscalar decay constant f(Ds)=(283 +/- 17 +/- 7 +/- 14) MeV. The errors are statistical, systematic, and from the D-s(+)->phi pi(+) branching ratio, respectively.